The work centers about three areas concerned with aldosterone regulation of ion transport. In the first area, the interaction of the steroid hormone, aldosterone, with receptors in various tissues is being investigated. The techniques of affinity chromatography and photo affinity labelling are utilized in an attempt to purify the aldosterone receptor. In the second area of investigation, the mechanism and regulation of sodium transport is being investigated in the urinary bladder of the toad. In the third area of investigation, the mechanisms and the regulation of urinary acidification is investigated. The role of carbonic anhydrase, bicarbonate stimulated ATP-ase, aldosterone and adaptation to chronic acidosis are under study.